Charles Darwin. Allen Grant

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СКАЧАТЬ and immutability of species, almost universal in the civilised world up to the end of the last century.

      Improbable as such a crude idea now seems to any person even moderately acquainted with the extraordinary variety and variability of living forms, it nevertheless contained nothing at all likely to contradict the ordinary experience of the everyday observer in the last century. The handful of plants and animals with which he was personally acquainted consisted for the most part of a few large, highly advanced, and well-marked forms, not in the least liable to be mistaken for one another even by the most hasty and casual spectator. A horse can immediately be discriminated by the naked eye from a donkey, and a cow from a sheep, without risk of error; nobody is likely to confuse wheat with barley, or to hesitate between classing any given fruit that is laid before him as a pear or an apple, a plum or a nectarine. Variability seldom comes under the notice of the ordinary passing spectator as it does under that of the prying and curious scientific observer; and when it comes at all, as in the case of dogs and pigeons, roses and hyacinths, it is no doubt set down carelessly on a superficial view as a mere result of human selection or of deliberate mongrel interbreeding. To the eye of the average man, all the living objects ordinarily perceived in external nature fall at once under certain fixed and recognisable kinds, as dogs and horses, elms and ashes, whose limits he is never at all inclined to confound in any way one with the other.

      Linnæus, the great father of modern scientific biology, had frankly and perhaps unthinkingly accepted this current and almost universal dogma of the fixity and immutability of species. Indeed, by defining a kind as a group of plants or animals so closely resembling one another as to give rise to the belief that they might all be descended from a single ancestor or pair of ancestors, he implicitly gave the new sanction of his weighty authority to the creation hypothesis, and to the prevalent doctrine of the unchangeability of organic forms. To Linnæus, the species into which he mapped out all the plants and animals then known, appeared as the descendants each of a solitary progenitor or of a primitive couple, called into existence at the beginning of all things by the direct fiat of a designing Creator. He saw the world of organic life as composed of so many well-demarcated types, each separate, distinct, and immutable, each capable of producing its like ad infinitum, and each unable to vary from its central standard in any of its individuals, except perhaps within very narrow and unimportant limits.

      But towards the close of the eighteenth century, side by side with the general awakening of the human intellect and the arrival of a new era of free social investigation, which culminated in a fresh order of things, there was developed a more critical and sceptical attitude in the world of science, which soon produced a notable change of front among thinking naturalists as to the origin and meaning of specific distinctions.

      Buffon was the first great biological innovator who ventured, in very doubtful and tentative language, to suggest the possibility of the rise of species from one another by slow modification of ancestral forms. Essentially a popular essayist, writing in the volcanic priest-suppressed France of the ancien régime, during the inconsistent days of Louis XV. and Louis XVI., when it was uncertain whether novel and heterodox opinions would bring down upon their author fame and reputation or the Sorbonne and the Bastille, Buffon was careful to put his conjectural conclusions in a studiously guarded and often even ironical form. But time after time, in his great discursive work, the 'Histoire Naturelle' (published in successive volumes between 1749 and 1788), he recurs anew to the pregnant suggestion that plants and animals may not be bound by fixed and immovable limits of species, but may freely vary in every direction from a common centre, so that one kind may gradually and slowly be evolved by natural causes from the type of another. He points out that, underlying all external diversities of character and shape, fundamental likenesses of type occur in many animals, which irresistibly suggest the novel notion of common descent from a single ancestor. Thus regarded, he says, not only the ass and the horse (to take a particular passage) but even man himself, the monkeys, the quadrupeds, and all vertebrate animals, might be viewed as merely forming divergent branches of one and the same great family tree. Every such family, he believed, whether animal or vegetable, might have sprung originally from a single stock, which after many generations had here developed into a higher form, and there degenerated into a lower and less perfect type of organisation. Granting this—granting that nature could by slow variation produce one species in the course of direct descent from another unlike it (for example, the ass from the horse), then, Buffon observed, there was no further limit to be set to her powers in this respect, and we might reasonably conclude that from a single primordial being she has gradually been able in the course of time to develop the whole continuous gamut of existing animal and vegetable life. To be sure, Buffon always saves himself from censure by an obvious afterthought—'But no; it is certain from revelation that every species was directly created by a separate fiat.' This half-hearted and somewhat subrisive denial, however, must be taken merely as a concession to the Sorbonne and to the fashionable exegesis of his own day; and, even so, the Sorbonne was too much in the end for the philosophic thinker. He had once in his life at least to make his submission and demand pardon from the offended orthodoxy of the Paris faculty.

      The wave of thought and feeling, thus apologetically and tentatively stirred on the unruffled pond of eighteenth century opinion by the startling plop of Buffon's little smooth-cut pebble, soon widened out on every side in concentric circles, and affected with its wash the entire world of biological science in every country. Before the close of the eighteenth century speculation as to the origin of species was rife in all quarters of Europe. In France itself, Geoffroy St. Hilaire, constitutionally cautious and undecided, but wide of view and free from prejudice, came slowly to the conclusion, in 1795, that all species are really derived by modification from one or more primitive types. In Germany, in the very same year, Goethe, with the keen vision of the poet and the calm eye of the philosopher uniquely combined, discerned independently as by a lightning flash the identical idea of the origin of kinds by modification of pre-existent organisms. 'We may assert without hesitation,' says that great nebulous thinker and observer, 'that all the more perfect organic natures, such as fishes, amphibians, birds and mammals, with man at their head, were formed at first on one original type, which still daily changes and modifies its form by propagation.' In England, twelve months earlier, Dr. Erasmus Darwin, Charles Darwin's grandfather (of whom more anon), published his 'Zoonomia,' a treatise on the laws of animal life, in which he not only adopted Buffon's theory of the origin of species by evolution, but also laid down as the chief cause of such development the actions and needs of the animals themselves. According to Dr. Erasmus Darwin, animals came to vary from one another chiefly because they were always altering their habits and voluntarily accommodating themselves to new actions and positions in life. His work produced comparatively little effect upon the world at large in his own time, but it had immense influence upon the next great prophet of evolution, Lamarck, and through Lamarck on Lyell, Charles Darwin, Herbert Spencer, and the modern school of evolutionists generally. We shall consider his views in greater detail when we pass from the spiritual to the physical antecedents of Charles Darwin.

      It was in 1801 that Lamarck first gave to the world his epoch-making speculations and suggestions on the origin of species; and from that date to the day of his death, in 1831, the unwearied old philosopher continued to devote his whole time and energy, in blindness and poverty, to the elucidation of this interesting and important subject. A bold, acute, and vigorous thinker, trained in the great school of Diderot and D'Alembert, with something of the vivid Celtic poetic imagination, and a fearless habit of forming his own conclusions irrespective of common or preconceived ideas, Lamarck went to the very root of the matter in the most determined fashion, and openly proclaimed in the face of frowning officialism under the Napoleonic reaction his profound conviction that all species, including man, were descended by modification from one or more primordial forms. In Charles Darwin's own words, 'He first did the eminent service of arousing attention to the probability of all change, in the organic as well as in the inorganic world, being the result of law and not of miraculous interposition. Lamarck seems to have been chiefly led to his conclusion on the gradual change of species by the difficulty of distinguishing species and varieties, by the almost perfect gradation of forms in certain groups, and by the analogy of domestic productions. With respect to the means of modification, he attributed СКАЧАТЬ